Microcapsules and concrete containing the same

ABSTRACT

Microcapsules, for inclusion in concrete, adapted to reduce the area of a defect by at least 45% in said concrete once a quantity of said microcapsules has ruptured, said micro-capsules each comprising: a polymeric shell encapsulating a liquid core, wherein the polymeric shell comprises a substantially impermeable polymer layer and the liquid core comprises carbonatogenic bacterial spores, and optionally bacterial nutrients, dispersed in a liquid medium. Also disclosed is a concrete composition comprising a quantity of such microcapsules, and a method of reducing the area of a defect in concrete.

The present invention relates to microparticles, especiallymicrocapsules, for inclusion in concrete or like materials, containingmicroorganisms in the form of bacterial spores and/or bacterialnutrients, which microparticles (e.g. microcapsules) are adapted toreduce the area of a defect in said concrete (or like material) once aquantity of said microparticles (e.g. microcapsules) hasfractured/ruptured. The invention also relates to a concrete or likematerial composition containing a quantity of such microparticles,especially microcapsules, which is “self-healing” in respect of anydefects therein.

Concrete, concrete-based and concrete-like materials are often used incivil engineering projects as the building material of choice because oftheir high compressive strength, high durability and low cost. Projectsin which such materials are used include constructions such as bridges,road projects, underground projects, water conservancy and hydropowerprojects, nuclear power plants, ports and marine engineering, etc, aswell as smaller scale projects such as ramps, paving slabs, etc.Constructions which include concrete or like materials typically havelong lifetimes (of at least 50 years), however, in this time frame usageand the influence of external environmental factors can lead to defectsforming therein. Defects include visible cracks (of millimetres inwidth), micro-cracks (of micrometres in width), indentations andcrevices. If left untreated, one or more of such defects could reducethe lifetime of a construction and/or may pose an immediate threat tothe safety of said construction and its users.

Although a concrete composition per se may be optimized to improve itsinherent defect resistance, for example by appropriate selection of theraw materials used, their mixing ratio, inclusion or omission ofparticular additives, the manufacturing process, casting processes andmethods, defects are known to still occur with varying degrees ofseverity and over the course of varying numbers of years since settingof the concrete. Therefore, the timely and effective repair of defectsin concrete and like material is of continued concern to those in thefield, including scientists and engineers.

It is known that under certain circumstances, some concrete compositionsmay exhibit a degree of autogenous healing, i.e. autogenous repair, ofdefects therein. Typically, with relatively freshly laid concrete andhigh strength concrete, un-hydrated cement particles are present in theconcrete matrix; when water becomes available in defects that may haveformed in such concrete, any un-hydrated cement particles present in/onthe defect begin to hydrate, leading to a certain degree of healing orrepair of the defect in question. In general, it is thought that thereare two mechanisms by which autogenous repair may occur based aroundsecondary hydration of un-hydrated cement particles present in theconcrete composition: (1) the consequential precipitation of calciumcarbonate, and (2) swelling of the hydration products to decrease thearea of the defect. With mechanism (1), carbon dioxide (CO₂) from thesurrounding atmosphere may dissolve in water to generate carbonateanions (CO₃ ²⁻) in the alkaline environment of the concrete (the pH ofconcrete is around 12.5˜13). Free dissolved calcium cations (Ca²⁺)arising from the defect may then react with the carbonate anions to formcalcium carbonate. However, any such autogenous healing is greatlydependent on the age of the concrete, the water to cement ratio and theavailable water in the vicinity of the defect.

It is also known, for example from EP2239242A1, to provide aself-repairing or “self-healing” concrete which has distributedthroughout a number of urea-formaldehyde, melamine-formaldehyde and/orurea-melamine-formaldehyde resin polymer microcapsules containingadhesive. The disclosed adhesives include mono-component adhesives, suchas polyurethanes, organo-silico anaerobes, acrylic resins, andchloroprene rubbers, and multi-component adhesives, such as epoxyresins. Once a crack occurs in the concrete, microcapsules in thevicinity of the crack rupture due to induced stress caused by the crack,releasing the encapsulated adhesive to repair the crack.

However, a number of technical problems may be encountered and require asolution to be provided with such teaching, including interfacecompatibility between the walls of the crack in the concrete and theadhesive materials used for repair, the extent to which the adhesivewill flow to repair the crack prior to it setting, the durability of theadhesive, and the consequential effects (such as localized weakening) onthe concrete immediately surrounding the repaired crack.

Accordingly, there is still a need to address the repair of defects inconcrete and like materials, preferably by means of auto-reparation soas to avoid the need for human or mechanical intervention in theidentification and actioning of a repair, in as timely a manner aspossible to provide a compatible and durable solution.

First Aspect

In a first aspect, the present invention thus provides microcapsules,for inclusion in concrete, concrete-based material and concrete-likematerial, adapted to reduce the area of a defect in said material once aquantity of said microcapsules has rupture or is exposed at an interfaceof the defect, said microcapsules each comprising:

a polymeric shell encapsulating a liquid core,

wherein the polymeric shell comprises a substantially impermeablepolymer layer and the liquid core comprises carbonatogenic bacterialspores dispersed in a liquid, and

wherein at least one of the following criteria (i)-(iii) is fulfilled:

-   -   (i) said polymer layer comprises a polymer selected from the        group consisting of: gelatines, polyurethanes, polyolef ins,        polyamides, polysaccharides, silicone resins, epoxy resins,        chitosan, aminoplast resins and derivatives and mixtures        thereof, and/or    -   (ii) said bacterial spores are in the form of a microorganism        that is capable of reducing the area of the defect by means of        mineral or extracellular polymeric substance (“EPS”) production,        and are preferably selected from the group of bacteria        consisting of: Bacillus cereus, Bacillus subtilis, Bacillus        sphaericus, Bacillus lentus, Bacillus pasteurii, Bacillus        megaterium, Bacillus cohnii, Bacillus halodurans, Bacillus        pseudofirmas, Myxococcus Xanthus and mixtures thereof, and/or    -   (iii) said liquid is a non-aqueous, water-immiscible liquid        selected from the group consisting of: organic oils, mineral        oils, silicone oils, fluorocarbons, fatty acids, plasticizers,        esters and mixtures thereof,        such that, when a quantity of said microcapsules is present in        the material, the area of the defect therein is reducible by at        least 45% as compared to an initial area of the defect once at        least some of said quantity of microcapsules have been ruptured.

Such microcapsules have the ability, once included in a concrete or likematerial composition, to reduce the area of a defect, such as a crack oran indentation therein, once a quantity of said microcapsules hasruptured. Rupture of the microcapsules is achieved by locally inducedinternal stress in the concrete around the area of the defect, however,an external influence such as force or increased/decreased temperature,may be applied in addition to the internal stress to act on the inherentfriability of the microcapsules to achieve rupture. Once ruptured, therelevant microcapsules will release their encapsulated contents, thusfacilitating repair of the defect in as timely a manner as possible toprovide a compatible and durable solution.

Microcapsules according to the invention may be made by any suitablemicroencapsulation technique known in the art, including, but notlimited to, coacervation, interfacial polycondensation polymerization,addition or in-situ emulsion polymerization, addition or in-sitususpension polymerization, spray-drying and fluidized bed-drying toproduce microcapsules of a desired size, friability andwater-insolubility. Generally, methods such as coacervation andinterfacial polymerization can be employed in known manner to producemicrocapsules of the desired characteristics. Such methods are describedin U.S. Pat. No. 3,870,542, U.S. Pat. No. 3,415,758 and U.S. Pat. No.3,041,288.

For the avoidance of doubt, the rupture of as few as a singlemicrocapsule would facilitate some degree of defect area reduction,however for the results to be non-negligible and for a discerniblereparation to be observed, a quantity of microcapsules (being greater innumber than a single microcapsule, preferably at least 10⁴ microcapsulesper cm² of defect area, and generally of the order of 10⁶ microcapsulesper cm² of defect area) are required to rupture.

Preferably, in microcapsules according to the first aspect of theinvention, any two of the three criteria (i)-(iii) may be fulfilled,with criteria (i) and (ii) being preferred. Further preferably however,in such microcapsules all three of criteria (i)-(iii) may be fulfilled.To achieve the percentage reduction in defect area discussed, in eachmicrocapsule, the concentration of the bacterial spores may preferablybe at least 10⁹ spores per gram (dry weight) of microcapsule.

Second Aspect

In a second aspect, the invention provides microcapsules, for inclusionin concrete, concrete-based material and concrete-like material, adaptedto reduce the area of a defect in said material once a quantity of saidmicrocapsules has ruptured or is exposed at an interface of the defect,said microcapsules each comprising:

-   -   a polymeric shell encapsulating a liquid core,    -   wherein the polymeric shell comprises a substantially        impermeable polymer layer and the liquid core comprises        carbonatogenic bacterial spores dispersed in a liquid, and    -   wherein, in each microcapsule, the concentration of the        bacterial spores is at least 10⁹ spores per gram (dry weight) of        microcapsule, such that, when a quantity of said microcapsules        is present in the material, the area of the defect therein is        reducible by at least 45% as compared to an initial area of the        defect once at least some of said quantity of microcapsules have        been ruptured.

The liquid in which the bacterial spores are dispersed may preferably bea non-aqueous, water-immiscible liquid.

As with the first aspect of the invention, such microcapsules have theability, once included in a concrete or like material composition, toreduce the area of a defect, such as a crack or an indentation therein,once a quantity of said microcapsules has ruptured, with all theattendant benefits described earlier. Again, such microcapsules may bemade by any suitable microencapsulation process, such as those describedearlier.

Advantageously, in either of the first or second aspects of theinvention, the liquid core of some or all of the microcapsules mayfurther comprise bacterial nutrients, i.e. the nutrients may beco-encapsulated with the carbonatogenic bacterial spores in some or allof the microcapsules. With such co-encapsulation, on rupture of arelevant microcapsule and dispersal of its contents, the bacterialnutrients are readily available to act with atmospheric oxygen andambient water to enable germination of the bacterial spores to formvegetative bacteria, thus facilitating calcium carbonate production, aswill described in more detail later in the specification. Furthermore,encapsulated nutrients may have a less detrimental effect on thesurrounding concrete matrix than if the nutrients were freelydistributed throughout.

Third Aspect

In a third aspect, the invention provides microcapsules, for inclusionin concrete, concrete-based material and concrete-like material, adaptedto reduce the area of a defect in said material once a quantity of saidmicrocapsules has ruptured or is exposed at an interface of the defect,said microcapsules each comprising:

-   -   a polymeric shell encapsulating a liquid core,    -   wherein the polymeric shell comprises a substantially        impermeable polymer layer and the liquid core comprises        carbonatogenic bacterial spores and bacterial nutrients        dispersed in a liquid medium.

In this third aspect of the invention, the nutrients are co-encapsulatedwith the carbonatogenic bacterial spores in the microcapsules,regardless of the concentration or variety of the bacterial spores(other than being carbonatogenic), the nature of the polymer layer andthe nature of the liquid medium.

As with each of the first and second aspects of the invention, suchmicrocapsules have the ability, once included in a concrete or likematerial composition, to reduce the area of a defect, such as a crack oran indentation therein, once a quantity of said microcapsules hasruptured, with all the attendant benefits described earlier. Again, suchmicrocapsules may be made by any suitable microencapsulation process,such as those described earlier.

In a preferred embodiment according to the third aspect of theinvention, when a quantity of such microcapsules is present in theconcrete or like material, the area of the defect therein may preferablybe reducible by at least 45% as compared to an initial area of thedefect once at least some of said quantity of microcapsules have beenruptured. To achieve the percentage reduction in defect area discussed,in each microcapsule, the concentration of the bacterial spores maypreferably be at least 10⁹ spores per gram (dry weight) of microcapsule.

Fourth Aspect

In a fourth aspect, the invention provides microcapsules, for inclusionin concrete, concrete-based material and concrete-like material, adaptedto reduce the area of a defect in said material once a quantity of saidmicrocapsules has ruptured or is exposed at an interface of the defect,said microcapsules each comprising:

-   -   a porous solid core, comprising a silica-based material, having        bacterial nutrients dispersed therein.

Surrounding said porous solid core, there may be provided a surroundingshell, which may also comprise a silica-based material, which may thesame as or different to the silica-based material of the core.

As with the previous aspects of the invention, such microcapsules havethe ability, once included in a concrete or like material composition,to reduce the area of a defect, such as a crack or an indentationtherein, once a quantity of said microcapsules has at least partiallyreleased its encapsulated nutrients, with all the attendant benefitsdescribed earlier. Again, such microcapsules may be made by any suitablemicroencapsulation process, such as those described earlier.

In a preferred embodiment according to the fourth aspect of theinvention, when a quantity of such microcapsules is present in theconcrete or like material, the area of the defect therein may preferablybe reducible by at least 45% as compared to an initial area of thedefect once at least some of said quantity of microcapsules have beenruptured or exposed at the crack surface. To achieve the percentagereduction in defect area discussed, the microcapsules may have come intocontact with humidity and/or water; the bacterial spores may be providedin accordance with any of the previous aspects if the invention and/orby a natural occurrence of such spores in the area surrounding theconcrete defect.

Fifth Aspect

In a fifth aspect, the invention provides microcapsules, for inclusionin concrete, concrete-based material and concrete-like material, adaptedto reduce the area of a defect in said material once a quantity of saidmicrocapsules has ruptured or is exposed at the interface of the defect,said microcapsules each comprising:

-   -   a porous solid core, comprising a carbohydrate-based material,        having carbonatogenic bacterial spores and/or bacterial        nutrients dissolved and/or dispersed therein.

Surrounding said porous solid core, there may be provided a surroundingshell, which may also comprise a carbohydrate-based material, which maythe same as or different to the carbohydrate-based material of the core.

As with the previous aspects of the invention, such microcapsules havethe ability, once included in a concrete or like material composition,to reduce the area of a defect, such as a crack or an indentationtherein, once a quantity of said microcapsules has at least partiallyreleased its encapsulated nutrients and/or bacterial spores, with allthe attendant benefits described earlier. Again, such microcapsules maybe made by any suitable microencapsulation process, such as thosedescribed earlier.

In a preferred embodiment according to the fifth aspect of theinvention, when a quantity of such microcapsules is present in theconcrete or like material, the area of the defect therein may preferablybe reducible by at least 45% as compared to an initial area of thedefect once at least some of said quantity of microcapsules have beenruptured or exposed at the crack surface. To achieve the percentagereduction in defect area discussed, the microcapsules may have come intocontact with humidity and/or water (and if not provided in themicrocapsules, the bacterial spores may be provided in accordance withany of the previous aspects of the invention and/or by a naturaloccurrence of such spores in the area surrounding the concrete defect).

Reducible Defect Area

With the microcapsules according to any of the previous aspects of theinvention, the area of the defect in the concrete or like material maybe reducible by at least 50%, preferably by at least 60%, furtherpreferably by at least 70% and most preferably by at least 80% ascompared to the initial area of said defect once at least some of saidquantity of microcapsules have been ruptured.

Advantageously, the reducible area of the defect may be determined after4 weeks of continuous wet-dry cycling, beginning with a wet phase whichcomprises immersion of the concrete or like material, or at least thesurface in which the defect is located, in water for 12-20 hours,preferably 16 hours, followed by a dry phase in which the concrete orlike material, or at least the surface in which the defect is located,in air (at ambient temperature, such as 20 ° C., at 50-70%, preferably60%, relative humidity) for 6-10 hours, preferably 8 hours. Suchconditions are believed to facilitate the at least 45 reduction indefect area discussed above.

Polymer Layer

The polymer layer of the microcapsules according to any of the previousaspects of the invention may comprise a polymer selected from the groupconsisting of: gelatines, polyurethanes, polyolefins, polyamides,polysaccharides, silicone resins, epoxy resins, chitosan, aminoplastresins and derivatives and mixtures thereof. These are the same polymersas for the first aspect of the invention. Many of these types ofpolymeric microcapsule shell materials are further described andexemplified in US3870542.

Preferably, the polymer layer of any of the aforementioned aspects ofthe invention comprises a polymer selected from the group consisting of:vinyl polymers, acrylate polymers, acrylate-acrylamide copolymers,melamine-formaldehyde polymers, urea-formaldehyde polymers and mixturesand derivatives thereof.

Highly preferred materials for the microcapsule shell wall areaminoplast polymers comprising the reactive products of, for instance,urea or melamine and an aldehyde, e.g. formaldehyde. The polymer layertherefore further preferably may be a melamine formaldehyde resin orinclude a layer of this polymer. Such materials are those which arecapable of acid-condition polymerization from a water-soluble prepolymeror precondensate state. Polymers formed from such precondensatematerials under acid conditions are water-insoluble and can provide therequisite microcapsule friability characteristics to allow subsequentrupture of the microcapsule. The microcapsule shell wall may furtherpreferably by formed by a cross-linked network of polymers comprising amelamine-formaldehyde : acrylamide-acrylic acid copolymer.

Microcapsules made from aminoplast polymer shell materials can be madeby an interfacial polymerization process, such as is described in U.S.Pat. No. 3,516,941: an aqueous solution of a precondensate (methylolurea) is formed containing from about 3% to 30% by weight of theprecondensate. A non-aqueous, water-immiscible liquid is dispersedthroughout this solution in the form of microscopically-sized discretedroplets. Whilst maintaining a solution temperature of between 20° C.and 90° C., acid is added to catalyze polymerization of the dissolvedprecondensate. If the solution is rapidly agitated during thispolymerization step, shells of water-insoluble aminoplast polymer formaround, so as to encapsulate, the dispersed droplets of liquid forming aliquid core. Microcapsules according to the present invention may beproduced by a similar method, with the carbonatogenic bacterial sporesand/or bacterial nutrients (as appropriate) being dispersed in theliquid core prior to polymerization.

The polymer layer comprised in the microcapsules of any of theaforementioned aspects of the invention may further comprise reactivefunctional groups, extending outwardly of the microcapsule, whereby themicrocapsule is chemically bondable within the concrete or likematerial. Such a reactive functional group preferably comprises areactive moiety adapted to provide covalent bonding within the concrete.

Silica-Based Materials

Suitable silica-based materials for use in accordance with any of theprevious aspects of the invention include those made from precursorssuch as sodium silicate and those selected from organically modifiedalkoxides (“ORMOSIL”) such as tetramethyl orthosilicate (TMOS),tetraethyl orthosilicate (TEOS), methyltrimethoxysilane (MTMS) andmixtures thereof. In general, the encapsulation process used may usesilicon precursors of Si—O—Si bonds employed in sol-gel processes. Tosuch silica precursors may be added colloidal silica nanoparticles (suchas Ludox^(lM) colloidal silica series), from 0 wt % to 10 wt % of thetotal silica content, to reinforce the shell and core structure of theobtained microparticles and/or microcapsules.

Many of these types of sol-gel microcapsules are further described andexemplified in EP2335818 A1, U.S. Pat. No. 7,255,874 and U.S. Pat. No.6,303,149.

Highly preferred precursors for microcapsulation are ORMOSIL comprisingthe reactive product of TMOS, TEOS and MTMS. Such materials are capableof acid-condition condensation in a compatible solvent or water-solublemonomers or precondensates. Silica-based microparticles and/ormicrocapsules formed from such monomers and/or precondensate materialsunder acid conditions may be partially to totally insoluble in thesolvents used and thus may provide the requisite microcapsule friabilityand/or porosity characteristics to allow subsequent release of thenutrients from microcapsules.

By way of example, the following describes the preparation of ORMOSILmicroparticles and/or microcapsules containing bacterial nutrients usinga sol-gel process:

-   -   dissolve from 0.1 g to 1 g of calcium nitrate and/or from 0.1 g        to 1 g of urea in 2 to 5 mL of a 2M hydrochloric acid aqueous        solution at room temperature;    -   dissolve from 0.01 g to 1 g of a polyethylene glycol sorbitan        monooleate surfactant (such as, for example TWEEN^(TM) 80) in        the above aqueous mixture;    -   optionally add a water suspended solution of colloidal silica        nanoparticles (such as Ludox^(lM) colloidal silica series), from        0 wt % to 10 wt % of the total silica content, to the above        aqueous mixture;    -   dropwise, add the above aqueous mixture to 20 mL to 100 mL of a        non-miscible organic solvent (such as cyclohexane, petroleum        ether) containing from 0.5 g to 4 g of a sorbitan monooleate        surfactant (such as Span^(TM) 80);    -   emulsify the resultant biphasic mixture with vigorous agitation        until the desired emulsion is reached;    -   dropwise, add from 1 to 4 mL of a commercial TEOS solution to        the above emulsion whilst mixing;    -   continue to stir at room temperature for the desired period of        condensation (from 1 to 24h);    -   filter and wash (with previous organic solvents) the resultant        silica-based microparticles and/or microcapsules to remove the        remaining surfactants, then dry.

Carbohydrate-Based Materials

Suitable carbohydrate-based materials for use in accordance with any ofthe previous aspects of the invention include those made from precursorssuch as sodium alginate and those selected from natural sourcecarbohydrate polymers (such as xanthan gums, arabic gums, agar,chitosan, pectin, pullulan, carrageenan, cellulosic materials),oligomers and mixtures thereof. In general, the encapsulation processesused may employ ionic exchange (exchange of sodium ions to calcium orbarium ions). To such carbohydrate-based precursors may be addedcolloidal silica particles (such as Ludox™ colloidal silica series),from 0 wt % to 10 wt % of the total silica content, to reinforce theshell and core structure of the obtained microparticles and/ormicrocapsules.

Many of these types of alginate microspheres are further described andexemplified in U.S. Pat. No. 5,766,907 A, U.S. Pat. No. 5,508,041 A andWO1991/009119A1.

The most highly preferred precursor for microcapsulation is sodiumalginate. Such a material may be capable of gelation and coacervation incompatible solvents. Gelatine-based microcapsules and/or microspheresformed from carbohydrate materials are partially to totally insoluble inthe used solvents and can provide the requisite microcapsule friabilityand/or porosity characteristics to allow subsequent release of thenutrients and/or bacterial spores from microcapsules.

By way of example, the following describes the preparation of sodiumalginate microparticles and/or microcapsules containing bacterialnutrients by a sol-gel or coacervation process:

-   -   dissolve from 0.1 g to 5 g of urea in 4 mL of water;    -   added from 1 to 5 wt % of sodium alginate powder to the above        and stir the mixture until a homogeneous viscous liquid is        obtained;    -   dropwise, add the above mixture to a calcium-containing solution        (preferably of calcium nitrate (for example 25 g/L) and        dissolved urea (to avoid a gradient of concentration that will        reduce the urea content of the microcapsules and/or microspheres        during the shell formation) and stir gently;    -   filter and dry the resultant alginate-based microparticles        and/or microcapsules.

The microcapsules obtained of any of the aforementioned aspects of theinvention may further comprise reactive functional groups on itssurface, extending outwardly thereof, whereby the microcapsule ischemically bondable within the concrete or like material. Such areactive functional group preferably comprises a reactive moiety adaptedto provide covalent bonding within the concrete.

Bacterial Spores

The bacterial spores of the microcapsules according to any of the secondto fifth aspects of the invention may be in the form of a microorganismthat is capable of reducing the area of the defect by means of mineralor EPS production, and may be preferably selected from the group ofbacteria consisting of: Bacillus cereus, Bacillus subtilis, Bacillussphaericus, Bacillus lentus, Bacillus pasteurii, Bacillus megaterium,Bacillus cohnii, Bacillus halodurans, Bacillus pseudofirmas, MyxococcusXanthus and mixtures thereof. Such carbonatogenic bacteria, i.e.carbonate- (CO₃ ²⁻) and bicarbonate- (HCO₃ ⁻) producing bacteria, may beused to generate calcium carbonate to achieve the desired concrete (orlike material) defect reparation, as will be discussed in more detailbelow.

Preferably, the bacterial spores of any of the aforementioned aspects ofthe invention may be selected from the group of bacteria consisting of:Bacillus sphaericus, Bacillus pasteurii and Bacillus cohnii as being thebest performing for present purposes in terms of carbonatogenesis.Further preferably, the bacterial spores may be selected from the groupof bacteria consisting of: Bacillus sphaericus and Bacillus pasteurii.

Liquid

The liquid, preferably a non-aqueous, water-immiscible, of themicrocapsules according to the second of third aspects of the inventionmay be selected from the group consisting of: organic oils, mineraloils, silicone oils, fluorocarbons, fatty acids, plasticizers, estersand mixtures thereof. By “non-aqueous” it is meant that the liquidcontains less than 0.1% by weight of water. By “water-immiscible” it ismeant that the liquid has less than 1% solubility in water (and viceversa), as this assists in the formation of the microcapsules by anemulsion polymerization route.

It is preferred that the liquid is a silicone oil, preferably having akinematic viscosity of 500 centistokes (mm²/sec) or less, preferably 350centistokes (mm²/sec) or less at 25° C.

Size & Content

Microcapsules according to any of the aforementioned aspects of theinvention may each have average dimensions in the range of from 1×10⁻⁷ mto less than 1×10⁻³ m, i.e. from 0.1 to less than 1000 μm, which may bespherical or non-spherical. Preferably, microcapsules may have anaverage diameter greater than 0.5 μm, preferably greater than 1 μm. Theaverage diameters of the microcapsules may, for example, fall in therange of from 0.5 to 900 μm, of from 0.5 to 500 μm, or of from 1 to 100μm.

Preferably, the bacterial spores dispersed in the liquid in eachmicrocapsule according to any of the aforementioned aspects of theinvention together may amount to 40-70 by volume of the volume withinthe polymeric shell of each microcapsule.

Further preferably, the bacterial spores may amount to at least 1%,preferably at least 2%, by volume of the volume of the liquid withineach microcapsule.

Bacterial Nutrients

By the term “bacterial nutrients” used throughout this specification, itis meant not only nutrients that may be required for germination and/orgrowth of bacteria, but also the calcium source used by the bacteria toprovoke formation of calcium-containing minerals, i.e. the “healing”ingredients. Bacterial nutrients described with respect to themicrocapsules of any of the aforementioned aspects of the invention maycomprise (but are not limited to): urea (CO(NH₂)₂), a suitable carbonand nitrogen source, such as nutrient broth, yeast, yeast extract,organic oil and a suitable source of calcium, such as hydrated calciumnitrate (Ca(NO₃)₂.4H₂O), calcium chloride, calcium acetate, calciumlactate and the like.

In addition to provision of novel and inventive microcapsules per se,the present invention also provides novel and inventive concretecompositions, which are “self-healing”, containing such microcapsules.

Advantageously, the bending strength of concrete, concrete-basedmaterial or concrete-like material compositions comprising saidmicrocapsules (such as described in the aspects and embodiments below)is not adversely affected by inclusion of said microcapsules as seen inthe examples. In embodiments are thus provided microcapsules adapted toprovide a composition bending strength when incorporated into aconcrete, concrete-based material or concrete-like material composition(such as described in aspects and embodiments below) of 90% or more,such as 95% or more, 98% or more, preferably 99% or more of acorresponding composition that is devoid of the microcapsules.

In embodiments, the microcapsules are adapted to provide a compositionbending strength when incorporated into a concrete, concrete-basedmaterial or concrete-like material composition comprising saidmicrocapsules (such as described in aspects and embodiments below) of atleast 4 MPa, such as at least 4.5 MPa, suitably at least 4.8 MPa (asmeasured according to a three-point bending test based on the standardNBN EN 12390-5 (2009) method as described in the examples section). Inembodiments, the microcapsules are adapted to provide a compositionbending strength when incorporated into a concrete, concrete-basedmaterial or concrete-like material composition comprising saidmicrocapsules (such as described in aspects and embodiments below) offrom 4 to 7 MPa, such as from 4.5 to 6.5 MPa, suitably, from 4.8 to 6.2MPa. Typically, these values are obtained when the microcapsules arepresent in the composition in a concentration of from 1% to 5% wt., suchas 1, 2, 3, 4, or 5% wt. relative to the weight of cement in theconcrete, concrete-based material or concrete-like material in thecomposition. In embodiments having a microcapsule dosage of around 1% byweight relative to the weight of the cement in the concrete,concrete-based material or concrete-like material in the composition,the bending strength may be at least 4.5 MPa, 4.8 MPa, or suitably atleast 5.0 MPa, such as from 4.5 to 6.0 MPa (such as from 4.8 to 5.5 MPa,e.g. around 5.2±0.3 MPa). In embodiments having a microcapsule dosage ofaround 3% by weight relative to the weight of the cement in theconcrete, concrete-based material or concrete-like material in thecomposition, the bending strength may be at least 5.0 MPa, 5.3 MPa, orsuitably at least 5.6 MPa, such as from 5.0 to 6.5 MPa (such as from 5.3to 6.2 MPa, e.g. around 5.9±0.3 MPa). In embodiments having amicrocapsule dosage of around 5% by weight relative to the weight of thecement in the concrete, concrete-based material or concrete-likematerial in the composition, the bending strength may be at least 4.5MPa, 4.8 MPa, or suitably at least 5.0 MPa, such as from 4.5 to 6.0 MPa(such as from 4.8 to 5.5 MPa, e.g. around 5.2±0.3 MPa) Bending strengthwas calculated according to a three-point bending test based on thestandard NBN EN 12390-5 (2009) method as described in the examplessection.

Advantageously, the inclusion of microcapsules may mean that concrete,concrete-based material or concrete-like material compositions (such asdescribed in the sixth to eighth aspects and embodiments) show adecreased open porosity compared to analogous compositions devoid of themicrocapsules, as detailed in the examples. Suitably the inclusion ofmicrocapsules in the compositions (such as described in the sixth toeighth aspects and embodiments above) therefore has a beneficial effectin reducing water absorption. Microcapsules of the invention may thussuitably provide a decrease in capillary water absorption and / or(preferably and) final saturated water absorption when incorporated intoconcrete compositions (such as described in the aspects and embodimentsbelow) compared to analogous compositions that are devoid of themicrocapsules.

In embodiments, the microcapsules are thus adapted to provide areduction in capillary water absorption in a concrete, concrete-basedmaterial or concrete-like material composition (such as described inaspects and embodiments below) compared to analogous compositions devoidof said microcapsules by at least 20%, suitably at least 25%, typicallyat least 30%, such as at least 35%, 40%, 45%, 50% or 55%. Typically,these values are obtained when the microcapsules are present in thecomposition in a concentration of from 1% to 5% wt., such as 1, 2, 3, 4,or 5% wt relative to the weight of cement in the concrete,concrete-based material or concrete-like material in the composition,such as at a microcapsule concentration of 1% wt., 3% wt. or 5% wt.,suitably 3% wt. and preferably 5% wt. of microcapsules relative to theweight of the cement in the concrete, concrete-based material orconcrete-like material in the composition. In embodiments, saidmicrocapsules are configured to reduce capillary water absorption by nomore than 60%, for instance, no more than 55%, 50%, 45% 40%, 35% or 30%compared to analogous compositions that are devoid of the microcapsules,particularly at a microcapsule concentration of 1% wt., 3% wt. or 5%wt., suitably 3% wt. and preferably 5% wt. of microcapsules relative tothe weight of the cement in the concrete, concrete-based material orconcrete-like material in the composition. In embodiments having amicrocapsule dosage of around 3% by weight relative to the weight of thecement in the concrete, concrete-based material or concrete-likematerial in the composition, the water absorption may be reduced by30-45% (such as 35-40%) relative to a composition devoid of themicrocapsules, or from 40-60%, preferably around 50%, e.g. 48% inembodiments having a microcapsule dosage of around 5% by weight relativeto the weight of the cement in the concrete, concrete-based material orconcrete-like material in the composition.

In embodiments, the microcapsules are thus adapted to provide concrete,concrete-based material or concrete-like material compositions (such asdescribed in aspects and embodiments below) having a capillary waterabsorption of 0.25 g/cm² or less, suitably 0.22 g/cm² or less, such as0.20 g/cm² or less, preferably 0.15 g/cm² or less, more preferably 0.13g/cm² or less at a time period of 72 h. Typically these values areobtained when the microcapsules are present in the composition in aconcentration of from 1% to 5% wt., such as 1, 2, 3, 4, or 5% wtrelative to the weight of cement in the concrete, concrete-basedmaterial or concrete-like material in the composition. Capillary waterabsorption may be calculated as described in the examples section.

In embodiments, the microcapsules are configured to provide a reductionin the saturated water absorption in said compositions compared toanalogous compositions devoid of microcapsules by at least 15% or 20%,suitably at least 25%, typically at least 30%, such as at least 35%,40%, 45%, 50% or 55%, such as at a microcapsule concentration of around1% wt., 3% wt. or 5% wt., suitably around 3% wt. and preferably around5% wt. of microcapsules relative to the weight of the cement in theconcrete, concrete-based material or concrete-like material in thecomposition. In embodiments, microcapsules are configured to provide areduction in the saturated water absorption in said compositionscompared to analogous compositions devoid of microcapsules by no morethan 60%, for instance, no more than 55%, 50%, 45% 40%, 35% or 30%,particularly at a microcapsule concentration of around 1% wt., 3% wt. or5% wt., suitably 3% wt. and preferably 5% wt. of microcapsules relativeto the weight of the cement in the concrete, concrete-based material orconcrete-like material in the composition. In embodiments having amicrocapsule dosage of around 3% by weight relative to the weight of thecement in the concrete, concrete-based material or concrete-likematerial in the composition, the water absorption may be reduced by20-30% (such as 20-25%, e.g. around 23%) relative to a compositiondevoid of the microcapsules, or from 30-50% (such as 33-38%), preferablyaround 36%, in embodiments having a microcapsule dosage of around 5% byweight relative to the weight of the cement in the concrete,concrete-based material or concrete-like material in the composition.

In particular embodiments, the microcapsules are thus adapted to provideconcrete, concrete-based material or concrete-like material compositions(such as described in aspects and embodiments below) having a saturatedwater absorption of 3.0% w/w or less, (i.e. weight water relative to thetotal weight of the composition), suitably 2.5% w/w or less, such as2.2% w/w or less, for instance 2.0% w/w or less, preferably 1.8% w/w orless, more preferably 1.6% w/w or less, even more preferably 1.5% w/w orless. Typically, these values are obtained when the microcapsules arepresent in the composition in a concentration of from 1% to 5% wt., suchas 1, 2, 3, 4, or 5% wt relative to the weight of cement in theconcrete, concrete-based material or concrete-like material in thecomposition. Saturated water absorption may be calculated as describedin the examples section.

Suitably, the microcapsules of the above aspects and embodiments may beconfigured to provide concrete, concrete-based material or concrete-likematerial compositions (such as described in aspects and embodimentsbelow) that exhibit hydration levels similar to those exhibited bycompositions devoid of microcapsules.

Sixth Aspect

Accordingly, a sixth aspect of the present invention provides aconcrete, concrete-based material and concrete-like material compositioncomprising:

-   -   a cementitious material, one or more aggregate materials, a        liquid binder and a quantity of microcapsules according to the        first, second, fourth and/or fifth aspects of the invention,    -   whereby, once set into concrete, the area of a defect therein is        reducible by at least 45% as compared to an initial area of the        defect once at least some of said quantity of microcapsules have        been ruptured.

Seventh Aspect

An seventh aspect of the present invention provides a concrete,concrete-based material and concrete-like material compositioncomprising:

-   -   a cementitious material, one or more aggregate materials, a        liquid binder and a quantity of microcapsules according to the        third, fourth or fifth aspects of the invention.

Eighth Aspect

A eighth aspect of the present invention provides a method of reducingthe area of a defect (as compared to an initial area of the defect) inconcrete, concrete-based material and/or concrete-like materialcomprising the steps of:

-   -   (i) providing a concrete, concrete-based material and/or        concrete-like material composition according to the sixth and/or        seventh aspects of the invention incorporating a quantity of        microcapsules;    -   (ii) setting the composition; and    -   (iii) causing at least some of said quantity of microcapsules to        rupture in response to the creation and/or worsening of a defect        in said set composition, thereby releasing their contents to        effect defect reduction.

Once set into concrete, the area of a defect therein may be reducible byat least 45 as compared to an initial area of the defect once at leastsome of said quantity of microcapsules have been ruptured.

The presence of microcapsules according to any of the aforementionedaspects of the invention into such concrete or like materialcompositions mean the area of a defect, such as a crack or anindentation therein, is reducible by at least 45% once a quantity ofsaid microcapsules has ruptured, i.e. a degree of self-repair isachievable. Rupture of the microcapsules is achieved by locally inducedinternal stress in the concrete around the area of the defect, however,an external influence such as force or increased/decreased temperature,may be applied in addition to the internal stress to act on the inherentfriability of the microcapsules to achieve rupture. Once ruptured, therelevant microcapsules will release their encapsulated contents, thusfacilitating repair of the defect in as timely a manner as possible toprovide a compatible and durable solution.

For the avoidance of doubt, the rupture of as few as a singlemicrocapsule would facilitate some degree of defect area reduction,however for the results to be non-negligible and for a discerniblereparation to be observed, a quantity of microcapsules (being greater innumber than a single microcapsule, preferably at least 10⁴ microcapsulesper cm² of defect area, and generally of the order of 10⁶ microcapsulesper cm² of defect area are required to rupture.

Surprisingly, the inventors found that the bacterial spores were able towithstand the manufacturing (e.g. microencapsulation) process, such thatthey were still able to germinate, and for ureolytic activity todecompose urea (present in bacterial nutrients) to begin. The bacterialspores thus remain dormant inside the microcapsules.

Without wishing to be bound by any theory, the repair mechanism isthought to follow the following pathway:

-   -   (1) Rupture of microcapsule→release of bacterial spores, for        exposure to germination activators: oxygen, water and bacterial        nutrients    -   (2) Germination of bacterial spores→production of vegetative        bacterial cells for use in hydrolysis    -   (3) Precipitation of calcium carbonate for defect repair via:        -   (a) CO(NH₂)₂+2H₂O→2NH₄ ⁺+CO₃ ²⁻[catalyzed by bacterial            urease]        -   (b) Ca²⁺+CO₃ ²⁻→CaCO₃

Defect formation, for example formation of a crack, triggers breakage ofthe microcapsules in the vicinity of the crack, which enables exposureof the liquid core. In the presence of oxygen, water and bacterialnutrients, the bacterial spores in the liquid core begin to germinate sothat ureolytic activity may begin. Urea is decomposed into CO₃ ²⁻ andNH₃/NH₄ ⁺ by the germinated bacteria (catalyzed by bacterial urease)under alkaline pH. When CO₃ ²⁻ ions meet with Ca²⁺ ions (e.g. fromcalcium nitrate), CaCO₃ is formed.

A concrete composition according to either the sixth or seventh aspectsof the invention is thus advantageous over prior art concretecompositions in that it possesses the desired interface compatibilitybetween the walls of a defect in the concrete and the in-situ generatedcalcium carbonate used for repair. Furthermore, there is no limit to theextent to which the in-situ generated calcium carbonate is generated toenable repair of the defect provided microcapsules are evenlydistributed throughout the concrete composition. Moreover, because ofthe compatibility of the repair material with the concrete, the repairpossesses the desired longevity and durability. Also, any consequentialeffects (such as localized weakening) on the concrete immediatelysurrounding the repaired crack are minimized, again because of thecompatibility of the repair material with the concrete.

The area of the defect in the concrete formable from the composition ofeither the sixth or seventh aspects of the invention may be reducible byat least 50%, preferably by at least 60%, further preferably by at least70% and most preferably by at least 80% as compared to the initial areaof said defect once at least some of said quantity of microcapsules havebeen ruptured.

Advantageously, the reducible area of the defect may be determined after4 weeks of continuous wet-dry cycling, beginning with a wet phase whichcomprises immersion of the concrete or like material, or at least thesurface in which the defect is located, in water for 12-20 hours,preferably 16 hours, followed by a dry phase in which the concrete orlike material, or at least the surface in which the defect is located,in air (at ambient temperature, such as 20 ° C., at 50-70%, preferably60%, relative humidity) for 6-10 hours, preferably 8 hours. Suchconditions are believed to facilitate the at least 45 reduction indefect area discussed above.

Advantageously, the bending strength of the concrete, concrete-basedmaterial or concrete-like material compositions of the inventioncomprising said microcapsules (such as described in the sixth to eighthaspects and embodiments above) is not adversely affected by inclusion ofsaid microcapsules as seen in the examples. In embodiments are thusprovided compositions wherein the bending strength of the composition is90% or more, such as 95% or more, 98% or more or preferably 99% or moreof a corresponding composition that is devoid of the microcapsules.

In embodiments, the composition has a bending strength (such asdescribed in aspects and embodiments below) of at least 4 MPa, such asat least 4.5 MPa, suitably at least 4.8 MPa (as measured according to athree-point bending test based on the standard NBN EN 12390-5 (2009)method as described in the examples section). In embodiments, thecompositions have a bending strength of from 4 to 7 MPa, such as from4.5 to 6.5 MPa, suitably, from 4.8 to 6.2 MPa. Typically, these valuesare obtained when the microcapsules are present in the composition in aconcentration of from 1% to 5% wt., such as 1, 2, 3, 4, or 5% wt.relative to the weight of cement in the concrete, concrete-basedmaterial or concrete-like material in the composition. In embodimentshaving a microcapsule dosage of around 1% by weight relative to theweight of the cement in the concrete, concrete-based material orconcrete-like material in the composition, the bending strength may beat least 4.5 MPa, 4.8 MPa, or suitably at least 5.0 MPa, such as from4.5 to 6.0 MPa (such as from 4.8 to 5.5 MPa, e.g. around 5.2±0.3 MPa).In embodiments having a microcapsule dosage of around 3% by weightrelative to the weight of the cement in the concrete, concrete-basedmaterial or concrete-like material in the composition, the bendingstrength may be at least 5.0 MPa, 5.3 MPa or suitably at least 5.6 MPa,such as from 5.0 to 6.5 MPa (such as from 5.3 to 6.2 MPa, e.g. around5.9±0.3 MPa). In embodiments having a microcapsule dosage of around 5%by weight relative to the weight of the cement in the concrete,concrete-based material or concrete-like material in the composition,the bending strength may be at least 4.5 MPa, 4.8 MPa, or suitably atleast 5.0 MPa, such as from 4.5 to 6.0 MPa (such as from 4.8 to 5.5 MPa,e.g. around 5.2±0.3 MPa). Bending strength was calculated by athree-point bending test based on the standard NBN EN 12390-5 (2009) asdescribed in the examples section.

Advantageously, compositions of the invention (such as described in thesixth to eighth aspects and embodiments above) show a decreased openporosity compared to analogous compositions devoid of the microcapsules,as detailed in the examples. Compositions of the invention thus suitablyshow a decrease in capillary water absorption and / or (preferably and)final saturated water absorption compared to analogous compositions thatare devoid of the microcapsules.

Suitably, the inclusion of microcapsules in the compositions (such asdescribed in the sixth to eighth aspects and embodiments above) has abeneficial effect in reducing the concrete porosity and thus reducingwater absorption. In embodiments, the capillary water absorption in thecomposition is reduced compared to analogous compositions devoid ofmicrocapsules by at least 20%, suitably at least 25%, typically at least30%, such as at least 35%, 40%, 45%, 50% or 55%, such as at amicrocapsule concentration of 1% wt., 3% wt. or 5% wt., suitably 3% wt.and preferably 5% wt. of microcapsules relative to the weight of cementin the concrete, concrete-based material or concrete-like material inthe composition. In embodiments, the capillary water absorption in thecompositions may be reduced by no more than 60%, for instance, no morethan 55%, 50%, 45% 40%, 35% or 30% compared to analogous compositionsthat are devoid of the microcapsules, particularly at a microcapsuleconcentration of 1% wt., 3% wt. or 5% wt., suitably 3% wt. andpreferably 5% wt. of microcapsules relative to the weight of cement inthe concrete, concrete-based material or concrete-like material in thecomposition. In embodiments having a microcapsule dosage of around 3% byweight relative to the weight of cement in the concrete, concrete-basedmaterial or concrete-like material in the composition, the waterabsorption is reduced by 30-45% (such as 35-40%) relative to acomposition devoid of the microcapsules, or from 40-60%, preferablyaround 50%, e.g. 48% in embodiments having a microcapsule dosage ofaround 5% by weight relative to the weight of the cement in theconcrete, concrete-based material or concrete-like material in thecomposition.

In particular embodiments, the compositions (such as described inaspects and embodiments above) have a capillary water absorption of 0.25g/cm² or less, suitably 0.22 g/cm² or less, such as 0.20 g/cm² or less,preferably 0.15 g/cm² or less, more preferably 0.13 g/cm² or less at atime period of 72 h. Typically these values are obtained when themicrocapsules are present in the composition in a concentration of from1% to 5% wt., such as 1, 2, 3, 4, or 5% wt. relative to the weight ofcement in the concrete, concrete-based material or concrete-likematerial in the composition. Capillary water absorption may becalculated as described in the examples section.

In embodiments, the saturated water absorption in the composition isreduced compared to analogous compositions devoid of microcapsules by atleast 15% or 20%, suitably at least 25%, typically at least 30%, such asat least 35%, 40%, 45%, 50% or 55%, such as at a microcapsuleconcentration of around 1% wt., 3% wt. or 5% wt., suitably around 3% wt.and preferably around 5% wt. of microcapsules relative to the weight ofthe cement in the concrete, concrete-based material or concrete-likematerial in the composition. In embodiments, the saturated waterabsorption in the compositions may be reduced by no more than 60%, forinstance, no more than 55%, 50%, 45% 40%, 35% or 30% compared toanalogous compositions that are devoid of the microcapsules,particularly at a microcapsule concentration of around 1% wt., 3% wt. or5% wt., suitably 3% wt. and preferably 5% wt. of microcapsules relativeto the weight of the cement in the concrete, concrete-based material orconcrete-like material in the composition. In embodiments having amicrocapsule dosage of around 3% by weight relative to the weight of thecement in the concrete, concrete-based material or concrete-likematerial in the composition, the water absorption is reduced by 20-30%(such as 20-25%, e.g. around 23%) relative to a composition devoid ofthe microcapsules, or from 30-50% (such as 33-38%), preferably around36%, in embodiments having a microcapsule dosage of around 5% by weightrelative to the weight of the concrete, concrete-based material orconcrete-like material in the composition.

In particular embodiments, the compositions (such as described inaspects and embodiments above) have a saturated water absorption of 3.0%w/w or less, (i.e. weight water relative to the total weight of thecomposition), suitably 2.5% w/w or less, such as 2.2% w/w or less, forinstance 2.0% w/w or less, preferably 1.8% w/w or less, more preferably1.6% w/w or less, even more preferably 1.5% w/w or less. Typically,these values are obtained when the microcapsules are present in thecomposition in a concentration of from 1% to 5% wt., such as 1, 2, 3, 4,or 5% wt. relative to the weight of cement in the concrete,concrete-based material or concrete-like material in the composition.Saturated water absorption may be calculated as described in theexamples section.

Suitably, the compositions of the above aspect and embodiments mayexhibit hydration levels similar to those exhibited by compositionsdevoid of microcapsules.

Microcapsule Dosage

Advantageously, the quantity of microcapsules comprised in thecomposition according to either the sixth or seventh aspects of theinvention, based on their dry weight, is in the range of 1% to 10%,preferably 2% to 8%, by weight of the cementitious material.

In one embodiment, the microcapsules may be added to the composition inthe form of an emulsion having the microcapsules dispersed therein,particular when the microcapsules have been formed by an emulsionpolymerization method. Further preferably, the emulsion may be awater-based emulsion.

Bacterial Nutrients

A concrete composition according to the sixth or seventh aspects of theinvention may comprise or further comprise bacterial nutrients, whichare preferably added to the concrete composition per se alongside thecementitious material, aggregate material, liquid binder andmicrocapsules, which may or may not themselves also contain bacterialnutrients.

The bacterial nutrients may be thus incorporated into the composition byany one or more of the following means:

-   -   by direct admixture into the composition;    -   by admixture of a quantity of different microcapsules containing        the nutrients;    -   by admixture of a hydrogel or other such suitable carrier, e.g.        porous aggregate, clays or diatomaceous earth, containing the        nutrients.

The quantity of bacterial nutrients comprised in the composition maybeneficially be in the range of 10% to 20%, preferably 12% to 18%, byweight of the cementitious material.

Concrete Ingredients

In a concrete composition according to the sixth and seventh aspects ofthe invention, the cementitious material is preferably cement. Atypically suitable cement is Portland cement, however any other suitablecementitious material may be used.

In a concrete composition according to the sixth and seventh aspects ofthe invention, the aggregate material is preferably a mixture of fineand coarse aggregates, of differing particles sizes, including materialssuch as sand, natural gravel, crushed stone and/or recycled materialsobtained from construction, demolition and/or excavation waste.

In a concrete composition according to the sixth and seventh aspects ofthe invention, the liquid binder is preferably water.

Advantageously, the ratio of cementitious material to aggregate materialto water in a concrete composition according to the sixth and seventhaspects of the invention may be in the ranges of (0.5 to 1.5):(1 to15):(0.1 to1), with the ratio 1:5:0.5 being preferred.

For a better understanding, the present invention will now be moreparticularly described by way of non-limiting examples only, withreference to the accompanying Figures in which:

FIG. 1 illustrates a series of plots (a) to (f) for a number ofdifferent cement samples (Groups R, N, C, NC, NCS3% and NCS5%respectively) of initial crack area (mm²) compared to final crack area(mm²) after being subjected to different incubation conditions (1) to(5);

FIG. 2 is a plot of the absolute value of healed crack area (mm²) forthe cement samples shown in FIGS. 1( a) to 1(f) for incubationconditions (1) to (5);

FIG. 3 is a plot of the healing ratio for the cement samples shown inFIGS. 1( a) to 1(f) and FIG. 2 for incubation conditions (1) to (5);

FIG. 4 is a scanning electron microscope (SEM) micrograph of a quantityof aminoplast microcapsules according to one embodiment of theinvention;

FIG. 5 is an SEM micrograph of the quantity of aminoplast microcapsulesshown in FIG. 4 but at greater magnification;

FIG. 6 is an SEM micrograph of a quantity of silica-based materialmicrocapsules according to another embodiment of the invention;

FIG. 7 is an SEM micrograph of an alginate microparticle according to afurther embodiment of the invention;

FIG. 8 is a plot of the absolute concentration of bacterial cellsagainst time (hours) for varying concentrations (g/L) of nutrient at afixed concentration (g/L) of urea; and

FIG. 9 is a series of plots (a) to (c) showing the degree of bacterialspore germination under different temperature conditions (28° C., 20° C.and 10° C. respectively) by measuring the concentration (g/L) of ureadecomposed over time (days) for varying concentrations (g/L) of nutrientat a fixed initial concentration (g/L) of urea.

FIG. 10 shows microscopy images taken before (FIG. 10 a) and after (FIG.10 b) mixing of microcapsules with concrete as described in example d).The images were acquired from a sample taken from the 5% sample asdescribed in example d).

FIG. 11 shows the bending strength data for cement samples having nomicrocapsules (reference “R”), as well as samples containing 1%, 3% and5% wt. microcapsules, respectively (relative to the weight of cement inthe concrete) as detailed in example e).

FIG. 12 shows the capillary water absorption data in g/cm² against timein hours for cement samples having no microcapsules (reference “R” -upper line with diamond points), 1% wt. microcapsules (second line totop with square points), 3% wt. microcapsules (third line to top withtriangular points) and 5% wt. microcapsules (bottom line with circularpoints), respectively (relative to the weight of cement in the concrete)as detailed in example f).

FIG. 13 shows the saturated water absorption data provided as weightwater versus total weight concrete sample against time in hours forcement samples having no microcapsules (reference “R” - upper line withdiamond points), 1% wt. microcapsules (second line to top with squarepoints), 3% wt. microcapsules (third line to top with triangular points)and 5% wt. microcapsules (bottom line with circular points),respectively (relative to the weight of cement in the concrete) asdetailed in example f).

FIG. 14 shows hydration heat production data as heat production rate(J/gh) plotted against time (minutes) for three samples having differentmicrocapsule concentrations (no microcapsules, i.e. sample “R”, 3% wt.microcapsules and 5% wt. microcapsules relative to the weight of cementin the concrete) prepared as in example g). The graph shows cumulativeheat production data (lines progressing to top right) and heatproduction rate (lines peaking on left and fall to bottom right). Forthe cumulative heat production data, R is the top of the three lines atthe top right of the graph, 3% is the middle and 5% is the bottom, Forthe heat production rate date, looking at the peak at the left of thegraph, R is the top of the three lines, 3% is the middle and 5% is thebottom.

FIG. 15 shows a schematic diagram of the three-point bending test asdescribed in example e) wherein 1 is the loading roller; and 2 and 3 aresupporting rollers.

EXAMPLES

a) Self -Healing Tests

Six example cement compositions were prepared, as detailed in Table 1below. The “Group R” specimens are the control specimens, preparedwithout any additions to the basic cement, sand and water composition.The “Group N” specimens were prepared with bacterial nutrients of (i)yeast, (ii) urea and (iii) calcium nitrate tetrahydrate in amounts of0.85%, 4% and 8% by weight of cement as the only additions as comparedto the control specimens. The “Group C” specimens were prepared withcontrol microcapsules (containing no bacterial spores) in an amount of3% by weight of cement. Thus the “Group NC” specimens were prepared asper the “Group N” and “Group C” specimens combined, with both bacterialnutrients and 3% by weight of microcapsules containing no bacterialspores. The “Group NCS3%” and “Group NCS5%” were prepared containingbacterial nutrients (as per the “Group N” specimens) and 3% and 5% (byweight of cement) respectively microcapsules containing encapsulatedbacterial spores in a concentration of 10⁹ spores per gram (dry weight)of microcapsule.

TABLE 1 Bacterial Microcapsule Dry Weight of Cement Sand Water NutrientsEmulsion Microcapsules Bacterial Group (g) (g) (g) (g) (g) (g) Spores? R450 1350 225 0 0 0 N N 450 1350 214 57.84 0 0 N C 450 1350 212.4 0 26.113.5 N NC 450 1350 201.4 57.84 26.1 13.5 N NCS 450 1350 192.8 57.84 34.713.5 Y 3% NCS 450 1350 178.7 57.84 57.84 22.5 Y 5%

In the specimens having bacterial nutrients added (Groups N, NC, NCS3%and NCS5%), to offset the 30.5 wt % provided by the water of hydrationin the calcium nitrate tetrahydrate, the amount of water added to thecomposition was accordingly reduced from 225 g. Similarly, in thespecimens having microcapsules added (Groups C, NC, NCS3% and NCS 5%),to offset the water provided from the emulsion (in which themicrocapsules were added to the compositions), the amount of water addedto the composition was accordingly reduced, or further reduced, from 225g.

For each of the six composition groups, five long reinforced prisms(having dimensions of 30×30×360 mm, with the internal rebar having alength of 660 mm and a diameter of 6 mm) were made—thus thirty specimensin total. After casting, the moulds were placed in an air-conditionedroom (at 20° C., >90% RH). The specimens in control

Group R were de-moulded after 24 hours, while the specimens of otherGroups were de-moulded after 48 hours because of their slower hardeningin the first 24 hours due to the additives. After de-moulding, allspecimens were stored in the same air conditioned room until the time oftesting.

28 days after casting, each of the long reinforced prisms were subjectedto a tensile test to create multiple cracks. The rebar of the prism wasclamped into a test machine (Amsler 100, SZDU 230, Switzerland), withthe distance between the clamp and the side surface of the prism being50 mm. After unloading, the rebar was cut off (leaving around 140 mmprotruding from each end of the prisms) and the remaining rebar waswrapped with aluminium tape to prevent iron corrosion during subsequentimmersion.

After crack creation, the long reinforced prisms were subjected to fiveincubation conditions:

-   -   (1) 20° C., >90% RH    -   (2) full and continuous immersion in water    -   (3) full and continuous immersion in a deposition medium    -   (4) continuous wet-dry cycling with water    -   (5) continuous wet-dry cycling with the deposition medium.

The deposition medium was composed of 0.2 M urea and 0.2 M Ca(NO₃)₂.

During the wet-dry cycles, the specimens were immersed inwater/deposition medium for 16 hours and then exposed to air for 8hours. The incubation conditions of (2), (3), (4) and (5) were performedin an air-conditioned room (20° C., 60% RH). When the specimens weresubjected to immersion, they were not in contact with the bottom of theimmersion container but some distance (about 5 mm) was maintained inbetween. Four 360 mm x 30 mm surfaces were named A, B, C and D torepresent different contact conditions with water: surfaces B and C werethe upper and lower surfaces, while surfaces A and D were the two sidesurfaces, respectively.

The cracks formed in each specimen, per incubation condition, wereidentified and counted; the results are shown in Table 2 below.

TABLE 2 Total No. No. of Cracks per Surface of Cracks Incubation SurfaceSurface Surface per Group Condition A B C Surface D Specimen R (1) 8 8 87 31 (2) 5 6 5 6 22 (3) 6 6 5 6 23 (4) 7 6 6 5 24 (5) 6 6 6 5 23 N (1) 66 5 6 23 (2) 6 7 6 7 26 (3) 7 5 5 6 23 (4) 8 7 8 8 31 (5) 6 6 6 6 24 C(1) 4 3 3 3 13 (2) 3 4 4 4 15 (3) 4 4 4 5 17 (4) 4 4 4 4 16 (5) 5 5 5 520 NC (1) 7 6 5 6 24 (2) 5 6 6 6 23 (3) 5 5 6 6 22 (4) 7 6 8 7 28 (5) 57 7 6 25 NCS3% (1) 10 7 9 9 35 (2) 4 6 6 4 20 (3) 10 9 7 6 32 (4) 7 4 67 24 (5) 5 5 5 5 20 NCS5% (1) 4 3 2 5 14 (2) 4 5 4 5 18 (3) 9 5 5 5 24(4) 4 9 7 7 27 (5) 9 7 5 5 26

Initial optical microscope images of the cracks in the specimens weretaken immediately after multiple cracking. Each crack was divided into10-11 portions by pencil markers to make sure the whole crack would bephotomicrographed with minimal overlap of the area among the images.

During the incubation period under different conditions, the specimenswere subjected to light microscopy every week in the first month and atthe end of the second month. The values of the initial and finalcracking area in the images were determined by a Leica^(TM) imageanalysis program.

Although the same methodology was applied to create cracks in each ofthe specimens, the cracking behaviour was clearly different due todifferent mechanical properties of the specimens, on account of theirdifferent compositions. As shown in Table 2, the number of cracks perspecimen varied from 13 to 35 and the crack widths varied from 50 μm to900 μm.

The self-healing efficiency, or extent of defect (crack) repair, of eachof the samples was evaluated by determination of the absolute healedcracking area (A_(h)).

Crack healing efficiency was also evaluated by the healing ratio (theamount of crack area filled by the precipitation), which was calculatedbased on the equation shown below. The healing ratio can indicate thepotential healing effect in the absence of specific information aboutthe cracks (widths, area, etc.) in practice.

$r = {\frac{A_{i} - A_{f}}{A_{i}} \times 100\%}$

where:

-   -   “r” is the crack healing ratio    -   “A_(i)” is the initial crack area (mm²)    -   “A₁” is the final crack area (mm²)

It was clearly observed that the crack area gradually decreased overtime. Within three weeks, the crack area was almost completely healed.However, in order to quantify the healing efficiency, the cumulativehealed crack area in each specimen after eight weeks was calculatedbased on its total initial (A_(i)) and total final (A₁) crack area,which is shown in accompanying FIG. 1.

As shown in FIG. 1, the crack area was decreased after eight weeks inall specimens (shown in plots (a) to (f)) except for those incubatedunder condition (1) (in an air-conditioned room at 20° C. at 95% RH), inwhich no obvious healing was visualized under light microscopy. In eachplot, a set of “paired” bars is plotted per incubation condition (1) to(5), with the total initial crack area (A_(i)) being represented by theleft hand bar in each pair, and the total final crack area (A₁) beingrepresented by the right hand bar in each pair.

The absolute value of the healed crack area (A_(h)) shown in FIG. 2provides a straight comparison of healing efficiency, while the healingratio (r) provides a means to compare healing efficiencies relative tothe original crack area per specimen as shown in FIG. 3.

Crack healing was observed in all specimens except for those stored at95% RH. For the specimens without microencapsulated bacteria, aconsiderable amount of crack healing (autogeneous healing) was observedwhen they were subjected to submersion or wet-dry cycles. The healedcrack area (A_(h)) varied from 12.6 mm² to 57.8 mm² depending on thespecific specimen and its incubation condition.

Compared with the specimens without encapsulated bacteria, those withmicroencapsulated bacteria showed much higher healing efficiency (r).The healed crack area (A_(h)) varied from 49.3 mm² to 80 mm². In view ofthe overall healed crack area, no significant difference was observedbetween the series of NCS3% and NCS5%, however, the specific healingefficiency of each specimen of NCS3% and NCS5% was different dependingon the incubation conditions. The maximum healed crack area (around 80mm²) was observed in the specimens which were subjected to the conditionof wet-dry cycles with water, although the specimens under otherincubation conditions exhibited similar healing efficiencies.

The crack healing ratio (r) in each specimen of the different series isshown in FIG. 3. The specimens without encapsulated bacteria had ahealing ratio (r) in the range of 18 to 50%. No significant differencein the overall healing ratio (r) was observed among different series (R,N, C and NC).

The specimens with microencapsulated bacteria had a much higher healingratio (r) which ranged from 48% to 80%. The highest value was obtainedin the specimen of NCS3%, which was subjected to incubation condition(4).

The specimens with microencapsulated bacteria incorporated showed muchhigher self-healing efficiency; around six times the crack area washealed compared with the control “Group R” series when the specimenswere subjected to incubation condition (4). In view of the healed crackarea, the specimens in non-bacterial groups (R, N, C, NC) had a healedarea range of 12.6 mm² to 57.8 mm² while the bacterial-containing groups(NCS3% and NCS5%) had 49.3 mm² to 80 mm² of the crack area healed. Themaximum crack width healed in the specimens of the bacterial-containinggroups was 970 μm, which was much wider than that in the specimens ofnon-bacterial groups (maximum 250 μm).

The micrograph of FIG. 4 shows a quantity of microcapsules having anaminoplast shell containing bacterial spores and bacterial nutrients inthe form of yeast extract. The magnified micrograph of FIG. 5 shows anumber of the quantity of said microcapsules having been ruptured, suchthat a number of bacterial spores along with its surround yeast extractis released from those number of microcapsules.

The SEM micrographs of FIGS. 6 and 7 respectively show a quantity ofmicroparticles/microcapsules having a silica-based material core and/orshell containing only bacterial nutrients and a microparticle ofalginate core material containing only bacterial nutrients.

b) Nutrient Effects on Spore Germination/Outgrowth

The plots shown in FIGS. 8 and 9 are a result of further investigativework undertaken to determine the effect of a particular bacterialnutrient (yeast extract “YE”) on the activity of bacterial spores, inparticular the germination and outgrowth of spores, and the subsequentformation of bio-precipitation.

FIG. 8 shows that, in a series of media with different concentrations ofyeast extract, the higher the concentration of yeast extract (from 0 g/Lto 20 g/L) for a given initial concentration of urea (“U”) (20 g/L), thehigher absolute concentration of bacterial cells present, particularlyafter a period of fifteen hours. Clearly, the outgrowth of spores wasmuch more remarkable at YE20/U20 and YE5/U20 than in other series withlower concentrations of yeast extract.

c) Temperature/Nutrient Concentration Effects on SporeGermination/Outgrowth

FIGS. 9( a), 9(b) and 9(c) show the variation in germination of B.sphaericus spores at different temperatures (28° C., 20° C. and 10° C.respectively) for different concentrations of yeast extract (m/n in thelegend indicates the concentration of yeast extract (“m”) and urea (“n”)respectively). As shown in FIG. 9( a), at 28° C., spores in the mediawith yeast extract concentrations of 20 g/L and 5 g/L exhibited a fasterrevival of ureolytic activity. From around 70% to around 95% of the ureain the media was decomposed in the first day. Spores in the media with 2g/L and 0.2 g/L yeast extract showed a greatly increased ureolyticactivity after 3 days. Within one week, all the urea in the media ofyeast extract was completely decomposed. For the spores in the mediawithout yeast extract, the revival of ureolytic activity was much slowerbut still gradually increased. About 50% (10 g/L) and 85% (17 g/L) ofthe urea was decomposed after 7 and 28 days respectively. Spores at 20°C. exhibited similar germination behaviour to those at 28° C., as shownin FIG. 9( b).

The revival of spores’ ureolytic activity was much slower at 10° C., asshown in FIG. 9( c). In the media with 20 g/L YE, about 3˜4 g/L of ureawas decomposed in the first 3 days. A significant increase of ureolyticactivity occurred between the 3rd and 7th days; 15˜17 g/L urea wasdecomposed by the 7th day. For the media with 5 g/L and 2 g/L YE, themajor revival of ureolytic activity occurred between the 7th and 14thdays and between the 14th and 21st days respectively. Urea wascompletely hydrolyzed after 21 days in the media with 20 g/L, 5 g/L and2 g/L YE. However, the spores in the media with 0.2 g/L and 0 g/L YEshowed no noticeable decomposition of urea within 28 days.

It thus appears that, especially when in an unfavourable environment,such as low temperature and in the presence of a high concentration ofcalcium ions, any negative effect on bacterial ureolytic activity may becounteracted by the presence of yeast extract (YE). Without yeastextract, bacterial spores could still germinate (but without outgrowth)and precipitate CaCO₃ ⁻, however precipitation formation was muchslower, and that the process only happened at moderate temperatures (20°C.-28° C., not at low temperatures).

d) Survival of Microcapsules in Concrete

A concrete composition described below in Table 3 was prepared. Based onthe standard EN 206-1, the w/c is 0.5, the content of cement is300kg/m³.

TABLE 3 Composition of the concrete mixture Per batch Per m³ Abs · v · mVolume (40 L) kg (kg/m³) (m³) kg Sand 0/4 730.00 2650 0.275 29.2Aggregate 2/8 526.00 2650 0.198 21.04 Aggregate 8/16 686.00 2650 0.25927.44 CEM I 52.5 N 300.00 3100 0.097 12.00 Water 150.00 1000 0.15 6.00

Four batches (40L per batch) of concrete were prepared by adding variousamounts of microcapsules to the above concrete composition. For this, amicrocapsule emulsion containing 40-50% wt. microcapsules, 5% wt. of ananionic surfactant and the remaining weight water (relative to the totalweight of the emulsion) was first formed before mixing with the concretemixture. The size of the microcapsules was from 3-20 μm.

The four compositions are represented below in Table 4. “R” is areference sample containing no microcapsules. The remaining batchescontained 1%, 3% and 5% microcapsules relative to the weight of thecement.

TABLE 4 Compositions of the concrete with or without microcapsulesSuper- Micro- Sand CEMI plasticizer Micro- capsule 0/4 AggregateAggregate 52.5N H₂O (mL/kg capsule emulsion (kg) 2/8 (kg) 8/16 (kg) (kg)(kg) cement) (kg) (kg) R 29.2 21.04 27.44 12.00 6.00 5 0 0 1% 29.2 21.0427.44 12.00 5.86 2.5 0.12 0.26 3% 29.2 21.04 27.44 12.00 5.58 5 0.360.78 5% 29.2 21.04 27.44 12.00 5.3 6 0.6 1.30

Microscopy images illustrated in FIG. 10 were taken before (FIG. 10 a)and after (FIG. 10 b) the mixing. It can be seen that after being mixedin concrete, most microcapsules survived the mixing process.

e) Concrete Strength—Bending Test

Samples of the four batches (R, 1%, 3% and 5%) as prepared in example d)were subject to a bending test after 28 days. For this test, prisms ofconcrete from the above batches R, 1%, 3% and 5% (100 mm x 100 mm x 500mm, n=3) were prepared and used. The results of the test are shown inFIG. 11. It can be seen that inclusion of the microcapsules did notsubstantially affect the tensile strength.

The bending test was conducted as follows: The concrete prisms (100mm×100 mm×500 mm) were subjected to a three-point bending test based onthe standard NBN EN 12390-5 (2009). As shown in FIG. 15, the spanbetween two support rollers was 320 mm. The load was applied in thecenter of the specimen by means of a server hydraulic jack with maximumload capacity of 100 kN.

The loading rate was determined by the formula:

$R = \frac{2 \times s \times d_{1} \times d_{2}^{2}}{3 \times I}$

where

R is the required loading rate, in N/s;

s is the stress rate, in MPa/s (N/mm².s);

d₁ and d₂ are the lateral dimensions of the specimen, in mm;

l is the distance between the supporting rollers, in mm; and

the flexural (i.e. bending) strength is calculated by the followingequation:

$f_{cf} = \frac{3 \times F \times I}{2 \times d_{1} \times d_{2}^{2}}$

where:

f_(cf) is the flexural (i.e. bending) strength, in MPa (N/mm²);

F is the maximum load, in N;

l is the distance between the supporting rollers, in mm;

d₁ and d₂ are the lateral dimensions of the specimen, in mm;

f) Water Absorption Test

Samples of the four batches (R, 1%, 3% and 5%) as prepared according toexample d) were subject to a water absorption test over 72 hours. Thedata are presented in FIGS. 12 and 13. As seen in FIGS. 12 and 13, thewater absorption (both capillary water absorption and final saturatedwater absorption) decreased after the addition of microcapsules. Asignificant decrease occurred for concrete having microcapsuleconcentrations higher than 1%. The capillary water absorption in theconcrete specimens was reduced by 39% and 48% at the microcapsule dosageof 3% and 5%, respectively. The saturated water absorption in the seriesof 3% and 5% was decreased by 23% and 36%, respectively. This means thatthe addition of microcapsules can beneficially decrease the openporosity of the concrete.

Capillary water absorption test: A modified capillary water absorptiontest based on RILEM 25 PEM 11-6 (NBN B 24-213) was performed. Theconcrete slices (100 mm×100 mm×60 mm) were cut from the concrete prismsand then were dried at 40 ° C. in an oven until weight changes were lessthan 0.1% at 24 h intervals. The initial weight of the specimens wasrecorded. Before the test, the four sides adjacent to the cuttingsurface (100 mm×100 mm) were wrapped by an aluminum tape to preventwater evaporation through the sides during the water absorption test.The initial weight of the wrapped specimens was also recorded.Subsequently, the specimens were brought into a water bath with a waterlevel of 10±1 mm and the cut surface facing downwards. At regular timeintervals (30 min, 1, 2, 3, 4, 5, 6, 24 h, 48h and 72 h), the specimenswere taken out from the water bath and weighed after removing thesurface water with a wet towel. After the measurement, the specimenswere immediately put back into the water bath. The test was done in anair-conditioned room with a temperature of 20° C. and a relativehumidity of 60%. The amount of water absorbed per unit (cm²) aftercertain time can be obtained using the following equation:

q _(i)=(Q _(t) −Q ₀)/S

where:

q_(t) is the amount of water absorbed per unit after certain time, ing/cm²;

Q_(t) is the weight of the specimens at time t;

Q₀ is the weight of the specimen at time 0;

S is the contact area with water, in cm².

Saturated water absorption test: After the capillary water absorptiontest, the concrete slices were taken out from the water bath and put inthe 40 ° C. oven until weight changes were less than 0.1% at 24 hintervals. Subsequently, the completely dry specimens were subjected tothe vacuum saturation test (NBN B 24-213). The specimens in dry statewere placed in a container and were subjected to vacuum for 3 h and thende-ionized water was added into the container till the specimens werecompletely immersed. The vacuum was maintained during water addition andlasted 1 h more at constant water level. After the vacuum was stopped,the specimens were kept submersed for another 12h. The final weight ofthe water saturated specimens was measured. The saturated waterabsorption was calculated by the following formula.

$W_{s} = {\frac{W_{w} - W_{d}}{W_{d}} \times 100\%}$

where:

W_(s): saturated water absorption ratio

W_(d): dry weight of the specimen

W_(w): wet weight of the water saturated specimen

g) Influence of Microcapsules on Cement Hydration

To investigate the influence of the microcapsules on cement hydration,hydration heat production was measured for various concrete samplesprepared as described below. Hydration heat production is used as anindicator for hydration degree. Three kinds of cement paste mixtures ofthe same water to cement ratio (0.5) were made: a reference cement pasteR, and cement pastes with p-capsules (3%), p-capsules (5%),respectively. The dosage of the additives was versus cement weight. Thehydration heat production (at 20° C.) was determined by a TAM AIRisothermal heat conduction calorimeter. The results are shown in FIG.14. It can be seen that the addition of microcapsules delayed somewhatthe appearance of the second hydration peak, the higher dosage used,more delay was observed. However, the cumulative heat production after 7days was quite similar for R, p-capsule 3% and p-capsule 5%, i.e. in therange of 355˜364 J/g. Thus, the difference is not significant. It can beconcluded that the microcapsules have no adverse effect on cementhydration.

Further Embodiments of the Invention

In a further aspect, the present invention provides microparticles, forinclusion in concrete, concrete-based material and concrete-likematerial, adapted to reduce, or to assist in the reduction of, the areaof a defect in said material once a quantity of said microparticles hasfractured or is exposed at an interface of the defect, saidmicroparticles each comprising:

-   -   a core, in the form of a porous solid and/or a liquid, having        carbonatogenic bacterial spores and/or bacterial nutrients        dissolved and/or dispersed therein.

Thus the core may be a porous solid, in which case it may or may not beprovided with a surrounding shell, i.e. there may be a shell whichsurrounds the porous solid core, or the core may be a liquid, it whichcase it may be provided with a surrounding shell, i.e. the shell mayencapsulate the liquid core therein. Alternatively, the core may be aporous solid having liquid present in substantially all of its pores,surrounding which there may be provided a surrounding shell.

For the avoidance of any doubt, said core may have carbonatogenicbacterial spores dispersed therein in the absence of any bacterialnutrients (which may be provided in the concrete or like material fromanother source), or said core may have bacterial nutrients dispersedand/or dissolved therein in the absence of any bacterial spores (whichmay be provided in the concrete or like material from another source),or said core may have both bacterial spores and bacterial nutrientsdissolved and/or dispersed therein. Once released, the bacterialnutrients are readily available to act with atmospheric oxygen andambient water to enable germination of the bacterial spores to formvegetative bacteria, thus facilitating calcium carbonate production, aswill described in more detail later in the specification

The “other source” of bacterial nutrients includes other microparticlescontaining said nutrients and naturally occurring, environmentalnutrients found in situ. The “other source” of carbonatogenic bacterialspores includes other microparticles containing said spores andnaturally occurring, environmental spores found in situ.

A “microparticle” as described herein is a particle with dimensions from1×10⁻⁷ m to less than 1×10⁻³ m, i.e. from 0.1 to less than 1000 μm,which may be spherical or non-spherical.

Such microparticles have the ability, once included in a concrete orlike material composition, to reduce, or assist in the reduction of, thearea of a defect, such as a crack or an indentation therein, once aquantity of said microparticles has fractured. Fracture of themicroparticles is achieved by locally induced internal stress in theconcrete around the area of the defect, however, an external influencesuch as force or increased/decreased temperature, may be applied inaddition to the internal stress to act on the inherent friability of themicroparticles to achieve fracture. Once fractured, the relevantmicroparticles will release their dissolved and/or dispersed contents,thus facilitating repair of the defect in as timely a manner as possibleto provide a compatible and durable solution.

In embodiments, said microparticles have a core provided with asurrounding shell. In embodiments, the core is a porous solid havingliquid present in substantially all of its pores.

In embodiments, the core comprises a silica-based material. Inembodiments, the core comprises a carbohydrate-based material.

In a further aspect is provided a concrete composition comprising:

-   -   a cementitious material, one or more aggregate materials, a        liquid binder and a quantity of microparticles as described        above.

In a still further aspect is provided a method of reducing the area of adefect in concrete, concrete-based material and/or concrete-likematerial comprising the steps of:

-   -   (i) providing a concrete, concrete-based material and/or        concrete-like material composition, such as described above,        incorporating a quantity of microparticles as described above;    -   (ii) setting the composition; and    -   (iii) causing at least some of said quantity of microparticles        to fracture in response to the creation and/or worsening of a        defect in said set composition, thereby releasing their contents        to effect defect reduction.

In the further aspects and embodiments above, the microparticles may bemicrocapsules according to any aspect or embodiment of the invention asdescribed herein. In the further aspects and embodiments above, thecomposition containing the microparticles may be as defined for any ofthe above aspects and embodiments containing microcapsules (i.e. whereinsaid microcapsules are microparticles as described above), In the methodabove, the method steps may be as defined according to methods relatingto microcapsules as disclosed above (i.e. wherein said microcapsules aremicroparticles as described above),

1.-39. (canceled)
 40. Microparticles, for inclusion in a concrete,concrete-based, or concrete-like material, said microparticles eachcomprising: a core, in the form of a porous solid and/or a liquid;carbonatogenic bacterial spores dissolved and/or dispersed in the core,wherein said microparticles are adapted to reduce, or to assist in thereduction of, the area of a defect in said material by carbonatogenesisby the carbonatogenic bacteria once a quantity of said microparticleshas fractured or is exposed at an interface of the defect. 41.Microparticles as claimed in claim 40, further comprising: a shellsurrounding the core.
 42. Microparticles as claimed in claim 41 whereinthe core of each of the microparticles comprises the porous solid. 43.Microparticles as claimed in claim 42, wherein liquid is present insubstantially all of the pores of the porous solid, and thecarbonatogenic bacterial spores are dispersed in the liquid andbacterial nutrients are dispersed or dissolved in the liquid. 44.Microparticles as claimed in 41, wherein the shell further comprises apolymer layer, the polymer further comprising melamine formaldehyderesin, the polymer having reactive functional groups, extendingoutwardly of the microparticle, whereby the microparticle is chemicallybondable within the material.
 45. Microparticles as claimed in claim 42wherein the porous solid of each of the microparticles comprises asilica-based material or a carbohydrate-based material. 46.Microparticles according to claim 40, wherein the microparticles aremicrocapsules, for inclusion in concrete, adapted to reduce the area ofa defect in said concrete once a quantity of said microcapsules hasruptured or is exposed at an interface of the defect, said microcapsuleseach comprising: a polymeric shell encapsulating a liquid core, whereinthe polymeric shell comprises a substantially impermeable polymer layerand the liquid core comprises carbonatogenic bacterial spores dispersedin a liquid, and wherein, in each microcapsule, the concentration of thebacterial spores is at least 109 spores per gram (dry weight) ofmicrocapsule, such that, when a quantity of said microcapsules ispresent in concrete, the area of the defect therein is reducible by atleast 45% as compared to an initial area of the defect once at leastsome of said quantity of microcapsules have been ruptured.
 47. Aconcrete, concrete-based, or concrete-like composition, comprising: acementitious material; one or more aggregate materials; a liquid binder;and a quantity of microparticles as claimed in claim
 40. 48. Thecomposition of claim 47, wherein the core of each the microparticles isprovided with a surrounding shell.
 49. The composition of claim 48,wherein the core of each of the microparticles comprises the poroussolid.
 50. The composition of claim 49, wherein liquid is present insubstantially all of the pores of the porous solid, and thecarbonatogenic bacterial spores are dispersed in the liquid andbacterial nutrients are dispersed or dissolved in the liquid.
 51. Thecomposition of claim 48, wherein the shell further comprises a polymerlayer, the polymer further comprising melamine formaldehyde resin, thepolymer having reactive functional groups, extending outwardly of themicroparticles, whereby the microparticles are chemically bonded to thecementitious material.
 52. The composition as claimed in claim 49wherein the porous solid of each of the microparticles comprises asilica-based material or a carbohydrate-based material.
 53. Thecomposition as claimed in claim 49 wherein the microparticles aremicrocapsules adapted to reduce the area of a defect in the compositiononce a quantity of said microcapsules has ruptured or is exposed at aninterface of the defect, said microcapsules each comprising: a polymericshell encapsulating a liquid core, wherein the polymeric shell comprisesa substantially impermeable polymer layer and the liquid core comprisescarbonatogenic bacterial spores dispersed in a liquid, and wherein, ineach microcapsule, the concentration of the bacterial spores is at least109 spores per gram (dry weight) of microcapsule, such that the area ofthe defect in the composition is reducible by at least 45% as comparedto an initial area of the defect once at least some of said quantity ofmicrocapsules have been ruptured.
 54. A method of reducing the area of adefect in a concrete, concrete-based, or concrete-like material, themethod comprising: providing a composition as claimed in claim 47;setting the composition; and causing at least some of said quantity ofmicroparticles to fracture in response to the creation and/or worseningof a defect in said set composition; effecting defect reduction in saidset composition by release of the contents of the quantity ofmicroparticles followed by carbonatogenesis by the carbonatogenicbacteria.
 55. The method of claim 54, wherein each of the microparticlesis provided with a surrounding shell.
 56. The method of claim 55,wherein the core of each of the microparticles comprises the poroussolid.
 57. The method of claim 56, wherein liquid is present insubstantially all of the pores of the porous solid, and thecarbonatogenic bacterial spores are dispersed in the liquid andbacterial nutrients are dispersed or dissolved in the liquid.
 58. Themethod as claimed in claim 54 wherein the porous solid of each of themicroparticles comprises a silica-based material.
 59. The method asclaimed in claim 54 wherein the porous solid of each of themicroparticles comprises a carbohydrate-based material.